1. Field
Certain embodiments relate to wireless communication systems, such as long term evolution advanced (LTE-A), which may be part of third generation partnership project (3GPP) LTE release 12 (Rel-12). More specifically, certain embodiments may provide an arrangement related to new carrier type for time division long term evolution (TD-LTE), which may also be related to Enhanced Interference Management and Traffic Adaptation.
2. Description of the Related Art
New carrier type (NCT) aims to provide improved energy efficiency, improved support for heterogeneous network (HetNet) and enhanced spectral efficiency. NCT operation can be based on demodulation reference signal (DM RS) and enhanced physical downlink control channel (EPDCCH), instead of common reference signal (CRS) and physical downlink control channel (PDCCH).
FIG. 1 shows a typical radio frame structure of new carrier type. As shown in FIG. 1, CRS, along with primary synchronization signal (PSS)/secondary synchronization signal (SSS), are transmitted only in every 5th subframe from one antenna port for the purpose of time/frequency tracking and synchronization as well as radio resource management (RRM) measurements. Spectral efficiency can be improved by minimizing legacy control signaling, such as PDCCH, PHICH, PCFICH, PBCH, and CRS. However, conventionally NCT is not backwards compatible, which means that legacy user equipment (UEs), such as those from Rel-8 to Rel-11, may not be able to operate in the NCT carrier at all.
Enhanced interference management and traffic adaptation (eIMTA) aims to enable more flexible time division duplex (TDD) uplink-downlink (UL-DL) reconfiguration for traffic adaptation in, for example, small cells. The eNodeB may vary UL-DL configuration relatively often, for those UEs configured to flexible UL/DL mode, compared to an existing situation where UL-DL configuration is in practice very stationary.
In eIMTA, there may be a predefined cell-specific UL/DL configuration broadcasted in the cell using system information block #1 (SIB-1). The legacy UEs (Rel-8 to Rel-11) in the cell may follow this configuration all the time. No new TDD UL-DL configurations are introduced. Rather, flexible TDD reconfiguration can only happen among existing (seven) configurations. FIG. 2 illustrates the available UL-DL configurations for TD-LTE (Rel-8/9/10/11).
Moreover, in eIMTA, TDD reconfiguration typically can occur with, at most, a single radio frame periodicity for those UEs configured to flexible UL/DL mode, although certain signaling solutions allow for selecting link direction separately for each scheduled subframe. The radio frame may be about 10 ms and consists of 10 subframes. In each UL-DL configuration there may be fixed subframes where the link direction is always predetermined. These fixed subframes are denoted as D (Downlink), S (Special) and U (Uplink) in FIG. 2. Additionally, as shown in FIG. 3, there may also be flexible subframes (denoted as F). Flexible (F) subframes can be used as D or U. The number of Flexible subframes may depend on the scenario, for example by SIB-1 configuration.
FIG. 3 illustrates a radio frame showing Downlink (D), Uplink (U) and Special (S) subframes according to exemplary SIB-1 configuration #0, as well as an exemplary set of flexible subframes available for Rel-12 UEs configured to flexible UL/DL mode.
Thus, FIG. 3 illustrates the basic settings. TDD configuration 0 is shown as an example, but the same principle can apply to other configurations as well. In addition to the SIB-1 configured UL-DL configuration, which defines whether a given subframe in the radio frame is downlink, special, or uplink subframe, in the case of flexible TDD UL-DL configurations some of the, for example, uplink subframes can be changed into downlink subframes.
Existing explanations of NCT, however, are limited to frequency division duplex (FDD) mode, rather than providing TDD specific aspects of NCT apart from some details on the reference signal and synchronization signal structure. Therefore, backwards compatibility related to NCT has not been addressed separately for FDD and TDD. Moreover, the combination of NCT and eIMTA is not conventionally known.